Direct Evidence that Vegans have Lower Cancer Rates

For decades, vegans have been saying that vegans have lower rates of cancer. Until now, there was no direct evidence for this. But last week a report from Adventist Health Study-2 was released showing vegans to have a lower cancer rate than regular meat-eaters. Unfortunately, there is not enough evidence to conclude that it is due to the diet.

There were 4,922 vegans in the study. After 4.1 years of follow-up and breaking the population into five categories (regular meat-eaters, semi-vegetarians, pesco-vegetarians, lacto-ovo vegetarians, and vegans) vegans had a 16% reduced risk of cancer when compared to regular meat-eaters (.84, .72-.99). Vegans were the only diet category to have a statistically significant lower risk of cancer.

These results were adjusted for age, race, family history of cancer, education, smoking, alcohol, age at menarche, pregnancies, breastfeeding, oral contraceptives, hormone replacement therapy, and menopause status. When the results were also adjusted for body mass index (BMI), the findings for vegans were no longer statistically significant (.86, .73 – 1.00). Additionally, the results were not adjusted for physical activity even though the authors found significantly more physical activity among those who did not get cancer and also among the vegans. Since physical activity could have affected the vegans’ BMI, you cannot rule out that it was simply more physical activity among the vegans that led to lower cancer rates and not the vegan diet.

When combining all the vegetarian categories and comparing them as a whole to the regular meat-eaters, the “vegetarians” had an 8% lower risk of cancer (.92, .85 -.99), but the “vegetarians” included some people who eat meat (the semi- and pesco-vegetarians). Using the BMI-adjusted model changed the finding a tad (.92, .85 – 1.00).

The follow-up period was only an average of 4.1 years – that’s not very long for a study on cancer. Hopefully, Adventist Health Study-2 will do some longer follow-up on cancer rates.

This entry was posted on Monday, November 26th, 2012 at 6:48 pm and is filed under Cancer. You can follow any responses to this entry through the RSS 2.0 feed.
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I got it from the following: “When combining all the vegetarian categories to the regular meat-eaters, the “vegetarians” had a 16% lower risk of cancer…” The difference between this group and the vegan group (at 17% reduced risk) is 1%. Am I missing something?

That’s true. It was .89 for pesco- and .86 for vegans after adjusting for BMI. I included the non-BMI adjusted version given that BMI and a vegan diet are closely correlated. I don’t mind it if the main reason that vegans would have a lower risk of cancer is due to their lower BMI. I would assume that is also primarily (though not entirely) the case for why vegans have a lower rate of type-2 diabetes.

I am part of this study, (even though I am not Adventist anymore, but I still espouse the beliefs of veganism, not smoking/drinking, and Sabbath rest) and have been for years now.
Yes, it did take into account smoking, alcohol and exercise. I get a questionnaire every couple years, and in the beginning, a HUGE questionnaire!

You can look at all the newsletters with simple graphs and articles here:

In the model that adjusted for BMI, the RR for vegans compared to meat eaters was 0.86 and this not statistically significant. Unlike Jack, I think that adjustment for BMI is needed in order to determine whether the reduced cancer rate is due to the diet.
It should also be noted that the study did not adjust the results to exercise or sedentary time.

PS: Jack, you have error in the RR for vegans: it is 0.84 (in the adjusted model without BMI) and not 0.83.

How dare you point out my total and complete ineptness? (Sigh.) It turns out I was looking at the footnotes for Table 4, not Table 3. So, not only did I use the wrong rate and CI, I thought that the BMI adjusted rate was still statistically significant and therefore, not really that big of a deal. Now that I have straightened it out (I hope), I have changed the post above and added a bit. I also added both adjustment models to the cancer article on VeganHealth.org.

You make a good point that physical activity wasn’t included and that could account for BMI difference – another thing I shouldn’t have overlooked. They adjusted for physical activity in their diabetes follow-up, so I wonder why they didn’t bother here.

So, the finding is not as impressive as I originally thought (and it wasn’t even all that impressive in my original thought, just enough to say that there was some evidence to claim vegans have a lower rate of cancer) so I wonder if I should make a follow-up post pointing out these errors.

I really don’t think there are health benefits of veganism independent of the nutrients we tend to eat more of and the toxins we tend to eat less of. By that, I mean that health conscious meat-eaters, who pay attention to their saturated fat intake as well as fiber and minerals, probably will fare the same as any vegan. However, as a group vegans have a disproportionate amount of health-conscious people who pay attention to nutrient intake.

Not to be a downer, but it makes me feel disingenuous to present this to the scientifically illiterate as evidence of the health benefits of veganism, and I feel that it can backfire. And yes, I know that the fear-mongering AGAINST veganism is worse than any exaggeration we could ever make in our favor, but two wrongs don’t make a right.

Idan Says: Kathleen Keene – do Adventists usually take b12 supplements ? do you take them?

Some do, I do sometimes. A lot of “hard core” Adventists need to take them, because just as “hard core” vegans don’t eat supplemented foods like soy milks or other processed foods like cereal, burgers, etc, and they mostly eat whole foods; those people would need to supplement. I am not in that hard core group, as I eat some veggie burgers, motherless milks, and other fortified foods.

There probably is a definitive answer to that question, as we were asked that question at some point on one of the questionnaires.

It should be put out there the percentages of people in the AHS-2 that are vegan, vegetarian, and so on.

Based on the analysis of 27 relevant food questions,
4.2% are total vegetarian,
31.6% lacto-ovo-vegetarian,
11.4% include fish (pescatarian),
6.1% are semi-vegetarian (eat meat <1 time/week) and
46.8% are non-vegetarian.
A wide distribution is also seen in the consumption of other foods; for instance, 25% drink soymilk several times per week and 66% eat nuts two or more times per week.

I think The China Study explains a much more important and comprehensive study involving many more people and it also explains how cancer is promoted in the body. I think this article is very misleading especially in its claim that this study was a ‘first’.

The China Study is important, yes. I love the book, and T. Colin Campbell. However, the Adventist Health Studies have been so enlightening in many ways. The first study showed that people who eat more fruits and vegetables have lower rates of cancer, and this was in the 70s. (AHS-1) This study is still referred to in major publications. Loma Linda University (the university that is undertaking this long term study) has made great advancements, and I look forward to them making more advancements with the incoming information.

I just sent in a questionnaire about a month ago, and this study has been going on since 2002. There are also way more people in the AHS than in the China Study. (about 96,000 in AHS-2, compared to 6,500 in the China Study.)

Yes, I am referring to the study done in China by T. Colin Campbell as well as the research he did in the Philippines before that.

I think the findings are more significant for comparing plant based/vegan diets with diets inclusive of animal products.

This study had 4% vegans and the participants were tracked for 4 years? and the vegans were included with other vegetarians to determine vegetarian vs non-vegetarian rates of cancer? It is hard to see how we get a clear picture of plant based/vegan vs animal based diets with that because so many ‘vegetarians’ rely heavily upon dairy and eggs.

I am certainly in favor of more research and studies. I just don’t see what is significant about this particular study when much more compelling evidence favoring plant based diet exists.

> and the vegans were included with other vegetarians to determine vegetarian vs non-vegetarian rates of cancer?

Only in one analysis. For the findings I primarily discuss in the blog post, the various diet groups were all separated from each other so they were comparing vegans to regular meat-eaters.

And when the China Study compares disease rates between counties, the counties they compare all include meat-eaters, and very few adjustments were made. From what I can tell, the China Study can also be considered cross-sectional. So even though 4 years isn’t very long, it’s 4 years as compared to merely a slice in time in the China Study.

This does not mean the China Study is wrong – it is what it is: a descriptive study finding lower animal product consumption in counties and also lower rates of chronic disease in those counties.